A major source of indoor allergy-causing proteins are dust mites. Dust mites, 100 to 300 microns in size, cannot be seen with the naked eye. Dust mite excrement, which is a key component that causes allergic reactions, is even smaller, ranging in size down to 10 microns. Thus, in order to be an effective barrier to dust, dust mites, and their allergy-causing particles, a fabric or material must limit the transmission of 10 micron particles through its planar surface. These facts are discussed, for example, in Platts-Mills TAE, et al., "Dust Mite Allergens and Asthma: Report of a Second International Workshop," J. Allergy Clin. Immunology, 1992, Vol. 89, pp. 1046-1060 ("Several studies have demonstrated that the bulk of airborne group I mite allergen is associated with the relatively `large` fecal particle, 10 to 40 Vm in diameter."); AllerGuard Pte Ltd. Website, 1996 ("The house dust mite cannot be seen with the naked eye, as it only measures 0.1 to 0.5 mm" [which corresponds to 100 to 500 microns]); and U.S. Pat. No. 5,050,256 to Woodcock, et al., (e.g., column 1, lines 44-46--"Ideally, if the mite barrier has pores, it should have a pore size generally less than 10 microns. It is apparent that anything smaller causes no allergic reaction."). The Platts-Mills and Woodcock documents each are entirely incorporated herein by reference.
The major concentration of dust mites in the home is found in the bedroom. For example, an average mattress can support a colony of 2 million dust mites. Pillows also are an excellent habitat for dust mites. Six-year old pillows typically have 25% of their weight made up of dust, dust mites, and allergen. Sofa cushions, chair cushions, carpets, and other foam or fiber filled articles also provide a suitable habitat for dust mites. In effect, every home contains many areas where dust mites can thrive.
Additionally, the presence of allergens from dust mites is a problem that increases as pillows, mattresses, and the like become older. During its lifetime, a typical dust mite produces up to 200 times its net body weight in excrement. This excrement contains the allergen that triggers asthma attacks and allergic reactions, including congestion, red eyes, sneezing, and headaches. The problem is exacerbated by the fact that it is difficult to remove dust mites from the materials in which they thrine. Pillows are rarely laundered, while most mattresses are never washed.
Commercially-available allergy-relief bedding products offer a wide array of claims regarding their efficacy as allergen barriers. These products are assumed to function as allergen barriers because they form an impervious film (as with the laminates) or because they are "tightly woven" (as with 300-count cotton sheeting) of because they have a pore size that is too small to permit allergen penetration (as with nonwovens).
Each of the above-noted products, however, has its own associated disadvantages. Laminated or coated materials typically are uncomfortable (due to little or no moisture vapor permeability), stiff, not soft to the touch, and noisy (i.e., make relatively loud, rustling noises when a person moves on the sheet or pillow). Additionally, while vinyl, polyurethane, and microporous coated fabrics are considered excellent barriers to allergens, they require venting when used as pillow or mattress tickings since air flow is not possible through these materials. U.S. Pat. No. 5,050,256 describes such a product. Pillows or mattresses covered with these materials cannot deflate and re-inflate when compressed, unless they are vented. The need to vent these fabrics, however, begs the question of whether they can be considered effective allergen barriers (as allergens can also enter and escape through the vents). Coated and laminated fabrics also tend to have a limited wearlife due to coating delaminator.
Uncoated cotton sheetings, although promoted as such, are not true barriers to) allergens due to their inherently large pore sizes. Allergy specialists routinely urge patients to launder their bedding products on a weekly basis. Such practices, however, only serve to further enlarge the pore size of cotton sheetings as fiber is lost with extended laundering.
Spunbond/meltblown/spunbond (SMS) polyolefin nonwovens used in mattress and pillow covers do provide a degree of barrier protection to allergens. SMS nonwovens also exhibit excellent air porosity. Their wearlife, however, is very short, particularly with hot laundering temperatures normally used by allergy sufferers. SMS nonwoven fabrics also have a significantly stiffer and harsher hand as compared with standard pillow tickings.
Other barrier products are known from the literature and are available on the market. For example, U.S. Pat. No. 4,822,667 issued to Goad et al. describes a reusable, launderable, sterilizable medical barrier fabric woven from 100% polyester fiber constructed of polyester yarn. This fabric is said to be blood and aqueous fluid transmission resistant, abrasion resistant, flame resistant, lint free, drapable, and sufficiently porous to eliminate heat build-up. The described material is used in medical garments, wraps, and sterilizable articles. This patent does not describe the use of the fabric as an allergen barrier. The Goad patent is entirely incorporated herein by reference.
U.S. Pat. No. 5,050,256 issued to Woodcock describes an allergen proof bedding system with a cover permeable to water vapor. As noted above, this patent is entirely incorporated herein by reference. The cover material described in this patent is made of Baxenden Witcoflex 971/973 type polyurethane-coated woven polyester or nylon fabric. This fabric is not air permeable; however, it does have a moisture vapor transmission ("MVT") rate of 2,500 to 7,000 g of water/m.sup.2 /day. Typically, the coated side of the fabric is on the inside of the sewn cover, and the seams are sealed. This product, however, has the disadvantages of coated or laminated materials described above.
U.S. Pat. No. 5,368,920 issued to Schortmann (International Paper Co.) describes a nonporous, breathable barrier fabric and related methods of manufacture. The fabric is a breathable barrier fabric created by filling void spaces in a fabric substrate with film-forming clay-latex material having a density range of 1,000 to 2,000 gm/l, to provide a barrier fabric permeable to water vapor and impermeable to liquids and air. The MVT rate ranges from 300 to 3,000 g/m.sup.2 /day. Applications include industrial, hospital, and other protective coverings. Again, this product has the disadvantages associated with coated and laminated fabrics, as described above.
Dancey, in U.S. Pat. No. 5,321,861, describes a protective cover for upholstered or padded articles, such as bedding, made from a microporous ultrafilter material having a pore size of less than 0.0005 mm. This material suppresses passage of fecal particles produced by house dust mites. To prevent particles from bypassing the ultrafilter material, the seams of the cover are welded, and its opening is sealed by a resealable fastener, such as a zip-fastener, covered with an adhesive tape.